Driving force of an automobile engine is transmitted to wheels through an intermediation of a power transmission system including any or all of a transmission, a propeller shaft, a differential, and a drive shaft.
In the power transmission system, there is used in many cases, as a bearing for supporting a shaft, a taper roller bearing excellent in load capability with respect to radial load and axial load, impact resistance, and bearing rigidity. As illustrated in FIG. 8, the taper roller bearing generally includes an inner race 2 having a tapered raceway surface 1 on an outer peripheral side thereof, an outer race 4 having a tapered raceway surface 3 on an inner peripheral side thereof, a plurality of taper rollers 5 arranged so as to be rollable between the inner race 2 and the outer race 4, and a retainer 6 for retaining the taper rollers 5 at predetermined circumferential intervals.
As illustrated in FIG. 9, the retainer 6 includes a pair of annular portions 6a and 6b and brace portions 6c for coupling the annular portions 6a and 6b with each other. The taper rollers 5 are accommodated in pockets 6d formed between the brace portions 6c adjacent to each other in a circumferential direction.
In the taper roller bearing, the taper rollers 5 and the respective raceway surfaces 1 and 3 of the inner race 2 and the outer race 4 are held in linear contact with each other, and the taper roller bearing is designed such that the respective raceway surfaces 1 and 3 of the inner and outer races and a roller center O accord with one point (not shown) on an axial center P (refer to FIG. 8).
Thus, the taper rollers 5 are pressed to a radially larger side when load acts thereon. In order to bear the load, a flange portion 7 protruding to a radially outer side is provided on a radially larger side of the inner race 2. Further, in order to prevent the taper rollers 5 from falling to a smaller end side until completion of the incorporation of the bearing into a machine or the like, there is provided a flange portion 8 protruding also to the smaller end side of the inner race 2.
In recent years, in accordance with an increase in in-vehicle space, progress has been made in reduction in size of an engine room, increased output of an engine, and a multi-stage transmission for less fuel consumption. Under the circumstances, the environment in which taper roller bearings are used becomes more severe each year. In order to meet the demand for life of the transmission under the use environment, it is necessary to achieve longer life of the bearing.
Under the above-mentioned circumstances, there has been proposed, to achieve longer life of the bearing, increasing the number of rollers or by increasing the length of the rollers so as to increase load capacity within the same dimension as that of the currently-used bearing. However, in the currently-used structure as described above, in terms of assembly of the bearing, the flange portion (small flange) 8 is provided on the radially smaller side of the raceway surface of the inner race 2. Meanwhile, the flange portion 8 imposes a restriction on an increase in the length dimension of the taper rollers 5. Further, the taper rollers 5 are retained by the retainer 6 as described above, and the brace portions 6c of the retainer 6 are interposed between the taper rollers 5 adjacent to each other in the circumferential direction. Thus, the brace portions 6c impose a restriction also on increasing the number of rollers. As described above, there has been conventionally a limitation on an increase in the load capacity.
Incidentally, in some conventional taper roller bearings, a flange portion (small flange) on a radially smaller side is omitted in an inner race (Patent Document 1). When the flange portion on the radially smaller side is omitted in the inner race, it is possible to secure a longer axial length of the taper rollers correspondingly to a size of the flange portion thus omitted, and hence possible to achieve an increase in the load capacity. However, when the flange portion on the radially smaller side is omitted in the inner race, the taper rollers 5 fall to the smaller end side before completion of the incorporation into a machine or the like. As a countermeasure, as illustrated in FIG. 6, in the bearing in which the flange portion (small flange) on the radially smaller side is omitted in the inner race, hook portions to be engaged with the flange portion 31 on the radially larger side are provided in the retainer so that the taper rollers do not fall off.
That is, the taper roller bearing illustrated in FIG. 6 is a double-row taper roller bearing, and includes a pair of inner races 21, an outer race 22, a plurality of taper rollers 23 arranged so as to be rollable between the pair of inner races 21 and the outer race 22, and a pair of retainers 24 for retaining the taper rollers 23 at predetermined circumferential intervals.
Similarly to the retainer 6 illustrated in FIG. 9, each of the retainers 24 includes a radially-larger-side annular portion 25, a radially-smaller-side annular portion 26, and brace portions 27 for coupling the radially-larger-side annular portion 25 and the radially-smaller-side annular portion 26 with each other. Pockets 28 are formed between the brace portions 27 adjacent to each other in a circumferential direction, and the taper rollers 23 are retained in the pockets 28, respectively.
In the radially-larger-side annular portion 25, there are formed hook portions 30 arranged at predetermined pitches in the circumferential direction. In this case, each of the hook portions 30 is constituted by a flat rectangular piece protruding from the outer peripheral end portion of the radially-larger-side annular portion 25 to the radially inner direction. Further, as illustrated in FIG. 7, in a flange portion 31 of each of the inner races 21, a cutout portion 32 is formed on a radially larger side of a radially outer surface 31a of the flange portion 31 of each of the inner races 21, and each of the hook portions 30 is engaged with the cutout portion 32. In this case, between the hook portions 30 and the cutout portions 32, there are slight gaps in an axial direction and a radial direction, which allow the retainers 24 to slightly move in the axial direction and the radial direction. In this context, the hook portions 30 are kept out of contact with the flange portion 31 when the retainers 24 in a neutral state with respect to the axial center during operation (in a bearing-assembled state) are kept out of contact with the same flange portion 31, and the hook portions 30 are brought into contact with the flange portion 31 while a bottom surface 31c of the flange portion 31 of each of the inner races 21 and an inner surface (radially inner end) 33b of each of the hook portions 30 are brought into contact with each other. The hook portions 30 effect hooking so that the inner races 21, the taper rollers 23, and the retainers 24 are maintained in the assembled state except during operation.    Patent Document 1: Japanese Utility Model Application Laid-open No. Sho 58-165324